The EM4 is a dual sensitivity magic eye tuning indicator, electrically identical to the EM34 (IO base). Mullard describe this device as suited to both receiver tuning indication and test equipment null indications. The grid voltage change is 0 - 5 volts and 0 - 16 volts. The display is viewed end on.

The Ct8 base was not a successful method of achieving long term low resistance contacts.

This valve has to be one of the most beautiful products of the technology and is a delight to behold.

The wide glass envelope is 25 mm in diameter and, excluding the Ct8 base contacts is 73 mm tall.

References: Datasheet & ¹⁰⁴³. Type EM4 was first introduced^¶ in 1939.

 
Pin Connections

Ct8	1	2	3	4	5	6	7	8
	-	h	h	k	a(1),a(d1)	g1	t	a(2),a(d1)

 
Absolute Maximum Operating Conditions^¶

CRT	Vh	Ah	Va	Vg	mAa
	6.3	0.2	250	-1	0.75

Thanks to Frank Philipse for supplying the above PDF datasheet

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